The invention relates to a system including a system for a motor vehicle including an air spring which encloses an air volume and a controllable shock absorber connected in parallel with the air spring. The invention also relates to a method for controlling such a system.
German patent publication 4,334,007 discloses a shock absorber spring unit wherein an air spring is connected in parallel with a controllable pneumatic shock absorber. The air spring is mounted above the pneumatic shock absorber and, when the air spring deflects, a piston is moved downwardly or upwardly in a chamber of the pneumatic shock absorber. The end face of the piston contains controllable throttle openings so that air can flow from a first component chamber into a second component chamber of the pneumatic shock absorber when there is an upward or downward movement of the piston. A damping of the shock absorber spring unit comes about because of the flow losses of the air flowing over in the throttle openings.
A large damping operation is performed with the shock absorber spring unit disclosed in German patent publication 4,334,007 and a system can be damped to a sufficient extent because an adequately large air flow is transferred via the throttle openings from one component chamber into the other component chamber when there is a movement of the piston. The shock absorber spring unit, however, does include the disadvantage that not only the damping but also the spring stiffness is influenced by the adjustment of the throttle in the end face of the piston. As a consequence of the above, only one of the two quantities can be pregiven independently of the other and the other quantity then results as a consequence thereof.
This leads to the condition that the spring stiffness of the shock absorber spring unit can be adjusted over a large range but the resulting damping does not correspond to the requirement of the vehicle for each throttle adjustment.
The slightest adjustable spring stiffness results when the throttle is opened entirely and the damping is then equal to zero.
The largest adjustable spring stiffness results for a throttle which is completely closed wherein no air flows over any longer and damping is also equal to zero.
Both conditions do not satisfy the requirements in the vehicle. One condition which does satisfy the requirements includes a throttle adjustment which lies therebetween and is only adjustable within a narrow range.
In summary, it can be stated that, in the shock absorber spring unit disclosed in German patent publication 4,334,007, the magnitude of the damping cannot always be adapted in a suitable manner to the spring stiffness of the entire shock absorber spring unit.
It is an object of the invention to provide a system which includes an air spring and a controllable shock absorber connected in parallel thereto wherein the damping is adaptable to the spring stiffness. It is also an object of the invention to provide a method for controlling such a system.
The system of the invention includes a system for a motor vehicle. The system includes: an air spring defining an enclosed air volume; a controllable shock absorber connected in parallel with the air spring; a structure defining an ancillary volume; and, a controllable throttle for controlling the passage of fluid between the enclosed air volume and the ancillary volume.
The method of the invention is for controlling a system including a system for a motor vehicle. The system includes an air spring enclosing an air volume and a controllable shock absorber connected in parallel to the air spring. The method includes the steps of: providing an ancillary volume connected to the air volume via a controllable throttle having a throttle resistance which can be varied; presetting a total damping of the system and a spring stiffness of the air spring; adjusting the throttle resistance so that the air spring has the preset stiffness; determining the magnitude of a damping which occurs at the controllable throttle in dependence upon frequency; and, adjusting the controllable shock absorber so that the sum of the damping occurring therein and the damping occurring at the controllable throttle corresponds substantially to the total damping.
Preferably, the total damping is so pregiven that the axle assembly and axle components are adequately damped in the entire frequency range. The frequency range includes at least the inherent frequencies of all components (which are capable of oscillation) of the system which should be damped; that is, especially the inherent frequencies of the assembly and of the axle components.
The advantages achieved with the invention are especially seen in that the total damping and the spring stiffness of the system can be pregiven independently of each other. A further advantage of the invention is that the inherent frequencies of the system can be continuously preset via the adjustment of the magnitude of the spring stiffness and via the adjustment of the damping which is independent thereof. A further advantage of the invention is that the air spring, which is connected to the ancillary volume, contributes to the total damping of the system and therefore the shock absorber has to provide a slighter damping for a preset total damping. The shock absorber can therefore be dimensioned to be smaller and less heat is developed in the shock absorber.
According to another feature of the invention, the ancillary volume is configured so as to be unchanged. The advantage of this embodiment is that an unchanged additional volume is especially easy to configure.
According to a first embodiment of the invention, the air spring and the shock absorber are each mounted alone. According to a second embodiment, the air spring and the shock absorber are mounted in a shock absorber spring unit. This affords the advantage that the system, which includes the air spring and the shock absorber, takes up only little mounting space. Preferably, the air spring is mounted above the shock absorber in this embodiment.
According to still another embodiment of the invention, the air volume of the air spring is connected via a line to the ancillary volume. According to an alternative embodiment of the invention, the air volume of the air spring is connected directly to the ancillary volume. In this case, the air volume of the air spring and the ancillary volume are delimited by a common partition wall in which the controllable throttle is mounted. The advantage of this embodiment is that the air spring and the ancillary volume, which is connected thereto, need only very little mounting space to accommodate the same.